A gaming server is a server that runs a service for a game, or couple of games, for example - a server that hosts a game so you will run it in multiplayer mode, a server that runs a website for a community and etc...The server needs to serve the client in order to give him the service, such as playing online with more people, and in this example, the server "connects" between the people even though they are not connected to each other, all of them are connected to the server.